Myopia is a rapidly growing problem throughout Asia, particularly in China, Japan, Singapore, and Taiwan, where it is reaching epidemic proportions. Even in the US and some countries in the EU (e.g. Italy), the incidence of myopia is significantly increasing. While most myopia is treatable with refractive correction, some patients with high myopia (>8 diopters) develop degenerative changes in the macula that cause central visual loss. These degenerative changes are not treatable with eyeglasses, contact lenses, or refractive corneal surgery (LASIK). Highly myopic eyes that succumb to degenerative myopia develop progressive scleral thinning and stretching of chorioretinal tissues leading to an outpouching (staphyloma) in the region of the posterior pole. While a staphyloma might develop in the fourth or fifth decade of life, often visual loss occurs 10-20 years later. Indeed, degenerative myopia is the leading cause of visual loss in many Asian countries. At present, there is no effective therapy to retard the progressive ocular axial elongation and scleral thinning that characterize the development of degenerative myopia.
A light adjustable lens (LAL) is an optically transparent optical device whose refractive properties can be changed after its fabrication and insertion into a human eye. Light adjustable lenses (LALs) can have a refraction modulating composition dispersed in a polymer matrix. After the lens has been implanted into the eye and refractive stabilization has occurred, the preexisting optical aberrations or those induced by the surgical procedure are measured. In order to correct these optical aberrations (e.g., spherical power, astigmatism, spherical aberration, etc.), a corresponding amount of UV-Vis radiation is applied to the LAL, which alters the optical properties of the lens either through changes in its shape, its index of refraction, or both. Following one or several irradiations in which portions of the lens have been exposed to selectively and spatially modify the refractive power, the entire lens is irradiated to “lock in” the modified lens.
Prior work describes the use of UV irradiation (320-400 nm) for post-operative power adjustment of LALs. For example, a Helium Cadmium (HeCd) laser operating at 325 nm and a mercury (Hg) arc lamp spectrally filtered for the emission lines at 334 and 365 nm have been used for modifying the refractive power of LALs. Additionally, the prior work also mentions tripled frequency laser diode pumped solid state YAG laser operating at 355 nm, an argon ion laser operating in between 350-360 nm, a deuterium discharge lamp, and broad band xenon:mercury lamps operating with any narrow band spectral filter are useful sources for conducting UV irradiation tests on light adjustable materials and lenses.
However, there are potential safety issues related to each of these sources. Coherent sources (e.g., lasers) are narrowly focused and have high irradiances that can cause permanent damage to retinal tissues. In addition, such sources must be rasterized across the lens requiring complex control of the beam and increased cost. Extended or more diffuse, incoherent sources such as arc lamps offer a more attractive solution from the standpoint of economic (cost and availability) and safety concerns (coherent vs. non-coherent) but they must be attenuated by as much as a factor of 1000 for use in irradiating the light adjustable lenses. Thus, improper use of the lamp, mechanical, or electrical failure could result in applying high irradiances and radiant exposures to the ocular structures causing damage. Taken together, there remains a need in the art for methods to modify the lens so as to increase the achieved power change, reduce the dose required for lock-in, and improve the retinal safety profile of the procedure.
Still further, refractive errors induced by progressive myopia may be corrected by eyeglasses, contact lenses, corneal refractive surgery, or intraocular lenses, but these methods provide only temporary relief and do not prevent visual loss induced by stretching of ocular tissues. Furthermore, current means to treat degenerative myopia are minimally effective. Various attempts have been made to arrest progression of myopia ranging from eyedrops to surgery have either minimal or no proven long term efficacy. Currently, there are no proven means to prevent the excessive ocular enlargement that occurs in degenerative myopia.
Degenerative myopia is often associated with scleral thinning and stretching, the causes of which are not completely understood, but reduction in the mechanical strength of the sclera is a contributory factor. Sufficiently increasing the tensile strength, or modulus, of the sclera would prevent ocular enlargement and reduce progression of myopia. Such a therapy will be useful not only in patients with incipient degenerative myopia, but also in patients with early onset myopia to prevent progression to higher magnitude refractive errors.
Given the limitations of current therapies for treating myopia, new therapies without such limitations are needed. The present invention addresses at least some aspects of this need.